Question 621881
As the time it takes to triple is 30 minutes, how many times will this happen in 2 hours? 
2 hours = 2 x 60 = 120 minutes

so 120/30 = 4

So the bacteria will triple four times in 2 hours.

3x500 + 3(3x500) + 3(3x3x500) + 3(3x3x3x500) = 1500 + 4500 + 13500 + 40500
= 60000